Lifting arm



FIG. 1 is a front perspective view of a lifting arm showing the claimed design;

FIG. 2 is a rear perspective view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left side view thereof;

FIG. 6 is a right side view thereof;

FIG. 7 is a top view thereof;

FIG. 8 is a bottom view thereof; and,

FIG. 9 is another right side view thereof in an environment in which it may be used.

The broken lines in FIG. 9 show environment that forms no part of the claimed design, and all other broken lines in FIGS. 1-4 and 8 show portions of the lifting arm that form no part of the claimed design. 

CLAIM The ornamental design for a lifting arm, as shown and described. 